Rolling bearing for linear movement having cage extending beyond outer sleeve

ABSTRACT

A ball bearing adapted for axial movement on a shaft is comprised of a cage having guideways defining endless paths having axially extending portions for loaded and unloaded balls, and semicircular end portions. An outer sleeve surrounds the central portion of the bearing and defines races for balls in the endless paths. End rings on the axial ends of the bearing radially outwardly cover the semicircular guideway portions. The semicircular guideway portions have outwardly convex bottoms, and the end rings have concave recesses in their inner surfaces aligned with the semicircular guideways. The convex portions of the guideways and the concave portions of the recesses have common centers of curvature extending parallel to the bearing axis and displaced outwardly therefrom.

BACKGROUND OF THE INVENTION

This invention relates to rolling bearings of the type generally adaptedfor axial movement with respect to a shaft, and is particularly directedto bearings of this type wherein a cage defining endless guideways forthe rolling elements, such as balls, is centrally surrounded by an outersleeve defining races for the balls, and surrounded at its ends by endrings.

Bearing structures of the above type are disclosed, for example, in U.S.Pat. No. 4,123,121 of the present applicants. In this arrangement, thecage is provided with a plurality of ball guides distributed about itsperiphery, each ball guide being comprised of a pair of axiallyextending guideways for loaded and unloaded balls, and a pair ofsemicircular reversing guideways interconnecting the axially extendingguideways. An endless row of balls is preferably provided in the ballguideways. The outer sleeve is coextensive with the axially extendingportions of the guideways, and defines races for balls in this portionof the guideways. The projecting ends of the guideways of the cage areradially surrounded by end rings, for example, of a plastic material.The cage may also be of a plastic material.

The present invention is directed to improvements in bearings of theabove type, wherein the components for the bearing may be easier andless expensive to produce, and are easier to assemble. In addition, theinvention is directed to ball bearing which are less subject to wear,particularly in the reversing zones, as well as to reducing noises inthe use of the bearings, and to making the bearings resilient withrespect to shaft deflection. The invention is further directed to amethod for producing such bearings. The invention is also directed tothe reduction of overall size of bearings of this type.

SUMMARY OF THE INVENTION

Briefly stated, in accordance with the invention, the above objectivesare achieved by providing a bearing structure of the previouslydescribed type, wherein the bottoms of the reversing guideway portionsof the cage extend convexly outwardly, and by providing concave recessesin the portions of the end rings disposed outwardly of the divergingguideways. The center of curvature of the convex portions of the bottomsof the cage are common with the center of curvature of the concaverecesses, these centers of curvature being on an axis extending parallelto the center axis of the bearing. In other words, the bottom of therecess in the end rings, starting from an axially oriented zenith lineof the recess, extend radially inwardly in the peripheral direction sothat the wall thickness of the end rings is reduced only over a narrowperipheral area; the end rings may be relatively thin walled in order toenable reduction of the radial dimension of the bearing of theinvention.

In accordance with a further feature of the invention, the recesses inthe end rings are axially open toward the outer sleeve of the bearing.As a consequence, the end rings may be readily axially slipped over thecage filled with balls, and fastened either to the cage or to the outersleeve by conventional techniques, such as by welding or the snapping ofprojections into corresponding grooves, holes or the like, so as tosecure the elements of the bearing against twisting. The end rings of abearing in accordance with the invention may thereby be produced bycasting or pressure molding processes in "open" molds, i.e., with axialslidable cores which can be formed without undercuts.

In accordance with a still further feature of the invention, the cagemay be produced by casting or pressure molding processes, employingradially slidable cores for molding the guideways for the loaded andunloaded balls, as well as for the two reversing guideways for thecorresponding row of rolling elements.

The guideways for the unloaded rolling elements may be disposed in thecage to be radially offset outwardly with respect to the guideways forthe loaded rolling elements. As a consequence, unloaded rolling elementsare carried in the guideways at a small distance from the shaft, so thatthere is no sliding contact between these unloaded rolling elements andthe shaft. The radially slidable cores for producing such guideways, inaccordance with the invention, are therefore movable in a directionrotated about the center axis of the bearing by an acute angle withrespect to the radial plane passing through the axis of the bearing. Inother words, the guide for the radially movable cores is slightlyrotated in order to readily enable the desired locating of the bottomsof the guideways. As a result, a uniformly small radial play of theballs in the reversing guideways can be provided that is independent ofthe size or size deviation of the angle of rotation of the individualslidable cores of casting or pressure molding molds, since the center ofcurvature of the concave recesses and the convex end ring bottomportions is located on the center axis about which the radially slidablecore is rotated. In addition, the same end rings may be employed,regardless whether or not such radial offset of the guideways for theunloaded rolling elements in the cage has been provided.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the invention will be more clearly understood, it will nowbe disclosed in greater detail with reference to the accompanyingdrawings, wherein:

FIG. 1 is a transverse cross-sectional view of a ball bearing inaccordance with the invention, taken along the lines B--B of FIG. 2;

FIG. 2 is a cross-sectional view, in a radial plane, of a portion of thebearing of FIG. 1, this view only showing one axial end of the bearing;

FIG. 3 is an end view of the bearing of FIG. 2, looking in the directionC, with the sealing element omitted;

FIG. 4 is a transverse cross-sectional view of a bearing in accordancewith the invention, taken along the line D--D of FIG. 2; and

FIG. 5 is a simplified diagramatic representation of a method forcasting or pressure molding of the cage of the ball bearing of FIGS. 1,and illustrating in a simplified manner the radially slidable core thatmay be employed in the process.

Referring now to the drawings, there is illustrated a rolling bearing ofthe type generally adaptable for relative axial movement with respect toa shaft, and comprised of a cage 1 in the form of generally elongatedcylindrical shell and fit within the bore of an outer sleeve 2. As willbe apparent in the following paragraphs, the outer sleeve 2 extends onlycoextensively with the axially central portion of the cage 1, and an endring 3 is provided radially surrounding the cage 1 at both of its ends.The end rings 3 may be identical.

In order to enable fastening of the end rings onto the cage, the endrings 3 may have radially inwardly directed projections 4, preferably atthe axial ends thereof away from the sleeve 2, the projections 4 fittinginto corresponding recesses 5 in the cage 1, as more clearly shown inFIGS. 2 and 3. The end rings may be permanently affixed to the cages,for example, by welding or any other conventional process, for exampleat the location of the projections 4. As more clearly seen in FIG. 2,the end rings 3 if desired may extend axially beyond the cage 1, andhave annular grooves 6a for receiving and holding a ring gasket 6adapted to also slide in contact with a shaft 7 on which the bearing ismounted. The shaft 7 is indicated in dot-dash lines in the drawings,since it does not form a part of the invention per se.

In the illustrated embodiment of the invention, the cage 1 is providedwith four axially extending guideways 10 having radially inwardlydirected slots, for accomodating rolling bearings under load, as well asfour axially extending guideways 11 for unloaded rolling elements. Theaxially extending guideways are provided only in the axial center of thecage. Semicircular guideways 13 at each axial end of the cage join pairsof guideways 10 and 11 at the ends thereof, to form continuous guidewaysin the cage. Thus, the cage accomodates, at its periphery, four endlessrows of rolling elements, such as balls, with the loaded balls 8 of eachendless row of balls rolling between the shaft 7 and the associatedaxially extending race 9 in the bore of the outer sleeve. Similarly,unloaded balls 18 roll in the unloaded guideways 11, as well as in thereversing guideways 13 of the cage, so that the balls may circulate intheir respective endless rows upon relative axial movement between thebearing and the shaft.

In accordance with one feature of the invention, the radial innersurfaces, i.e., bottoms 12, of the reversing guideways 13 are convexwhen viewed in a cross section extending transversely of the axis of thebearing, as more clearly shown in FIG. 1, wherein the bottoms 12 of thethese guideway portions have radii of curvature r and centers ofcurvature 16. The centers of curvature 16 are on an axis parallel to thecentral axis 15 of the bearing, and the axis 16 is radially displaced sothat the curvature of the bottoms 12 is greater than the curvature ofthe bore of the cage. In other words, the radii of curvature of theconvex surfaces of the bottoms 12 of the reversing guideways are lessthan the radius of curvature of the bore of the cage.

In order to accomodate the unloaded balls 18 in the reversing guideways13, the end rings 3 have cylindrical recesses 14 on their radial innersurfaces. These recesses preferably extend to the axial ends of the endrings toward the outer sleeve 2, but do not extend to the other axialends of the end rings. The recesses 14 are centered over the reversingguideways 13, and have centers of curvature that coincide with thecenter of curvature 16 of the corresponding reversing guideways. Theradius of curvature R of the recesses 14 is sufficiently large, ascompared with the radius of curvature r of the reversing guideways 13,that the balls may freely circulate in the guideways.

In the preferred embodiment of the invention, the guideways 11 forunloaded balls 18 are located in the cage 1 such that they are radiallyoffset outwardly, with respect to the guideways 10 for loaded balls 8,in order to enable the unloaded balls 18 to be spaced radially outwardlya short distance from the shaft 7, as shown in FIG. 4. For this purposeas shown in FIG. 4, the outer sleeve 2 may be provided with axiallyextending grooves 17 to define races for the balls 18 not under load.The races 9 for the balls under load may merely be defined by theinternal bore of the sleeve 2, as also shown in FIG. 4.

As a consequence of this radial offsetting of the guideways with respectto the central axis of the bearing, and the use of convex bottomsurfaces 12 for the reversing guideways, it is apparent that straightlines extending between the centers of the balls in the correspondingloaded and unloaded guideways will not be normal to the radial plane 20defined by the axes 15 and 16, and hence that an acute angle α willexist between the plane 20 and the plane 21 defined by the axis 16 andnormal to the distance between the centers of the loaded balls 8 andunloaded balls 18. In other words, the centers of the balls 8 under loadare farther from the radial plane 20 than the centers of the unloadedballs 18.

In accordance with the invention, the cage 5 may be formed of a plasticmaterial, such as by casting or pressure molding, and specifically by aninjection molding process as illustrated in FIG. 5. For this purpose, inorder to mold the axially extending guideways 10 and 11 and thereversing guideways 13 therebetween, the die (not shown) is providedwith a slidable core 19, which is adapted to be radially directed intoand out of the die cavity. The slidable core 19 may have symmetricalprojections 19a and 19b for forming the bottoms of the axially extendingguideways, the end of these elongated projections 19a and 19b preferablybeing semicircular in accordance with the desired shape for the bottomsof the guideways. The elongated portions of the projections 19a and 19bfor forming the axially extending guideways also preferably haveparallel sides, in order to facilitate their removal from the moldedcage. As a consequence, the sides 10a and 11a of the axially extendingguideways which were formed by these parallel sides of the slidable coreare also parallel, and are in planes at acute angles α to the plane 20defined by the axes 15 and 16. This is particularly true with respect tothe adjacent side walls 10a 10 b, as seen in FIG. 5, although it will beapparent that the guideway 11 may not be adequately deep that its otherside wall is formed by a parallel wall of the core. The slidable core 19of course is shaped to simultaneously form the reversing guideways 13.The slidable core 19 is thus mounted by conventional means in its die,for movement in a direction at an angle α with respect to the plane 20.

The radial sliding core 20, which may have symmetrical sides, mayconsequently be produced relatively simply and inexpensively. Due to theangular offset in the direction of movement of the core 19, the correctradial displacement the guideways 10 and 11 can easily be provided inthe cage, as desired.

The end rings 3 for the bearing in accordance with the inventionpreferably are identical, i.e., have identically formed recesses 14, sothat they may be affixed interchangably to either end of the bearing.This of course also simplifies the production of the bearing, andreduces its cost. Any variations in the magnitude of the angle α willnot result in narrowing of the reversing guideway in the cage, with theaccompanying danger of jamming other balls, since the center ofcurvature of the recesses 14 and the center of curvature of the bottomsurfaces 12 of the reversing guideways coincide.

The rolling bearing in accordance with the invention provides theadditional substantial advantage in that it may be produced with aminimum radius, since the recesses in the reversing guideways extendonly over relatively narrow peripheral regions of the walls of the endrings. As a consequence, the walls of the end rings covering thereversing guideways may be made very thin, without the necessarystrength of the end rings being impaired by the recesses. In addition,in accordance with the invention, the end rings may advantageously beformed of a plastic material, for example, by injection molding.

The outer sleeves may advantageously be of steel, for example either cutfrom a tube or deep drawn from a round blank.

While the invention has been disclosed and described with reference to asingle embodiment, it will be apparent that variations and modificationsmay be made therein. Thus, in place of the ring gasket 6, any other formsuitable gasket may be employed, such as a sealing flange acting as alabyrinth seal affixed to the end rings or integral therewith. The outersleeve may alternatively be circularly bent from strip steel, or mayotherwise be provided with an elongated slot so that radial play betweenthe shaft and the bearing may be varied to compensate for expansion orcompression as the bearing is mounted, for example, in a housing bore.In order to provide close contact between the rolling balls and theraces, both the axially extending race for the loaded balls and theaxially extending race for the unloaded balls may be formed as groovesin the outer sleeve, and these grooves may be formed in the outer sleeveif desired, by stamping, so that the grooves have cross sections adaptedto properly receive the balls.

It is therefore intended in the following claims to cover each suchvariation and modification as follows within the true spirit and scopeof the invention.

What is claimed is:
 1. In a rolling bearing adapted for relative axialmovement with respect to a shaft, and including a cage with axiallyextending pairs of first and second guideways for loaded and unloadedrolling elements respectively and circular reversing guideways at theaxial ends of and interconnecting each pair of first and secondguideways, to form continuous paths, endless rows of rolling elements insaid paths, and outer sleeve surrounding said cage and having an axiallength substantially equal to the lengths of said first and secondguideways, whereby the ends of said cage having said reversing guidewaysproject axially beyond said outer sleeve, and end rings mounted toradially outwardly cover said projecting ends; the improvement whereinthe radially inward surfaces of said semicircular guideways, withrespect to the axis of said bearing, are radially outwardly convex andsaid end rings have concave recesses in their inner surfaces andradially surrounding said semicircular guideways, the centers ofcurvature of said surfaces of each semicircular guideway and thecorresponding recess of said end ring being on a common axis parallel tosaid bearing axis, the centers of said second guideways being displacedradially outwardly in said cage from the centers of said firstguideways, whereby rolling elements in said second guideways are heldout of contact with said shaft.
 2. The rolling bearing of claim 1wherein said sleeve defines races for said rolling elements.
 3. Therolling bearing of claim 1 wherein said rolling elements are balls. 4.The rolling bearing of claim 1 wherein said cage and end rings are of aplastic material.
 5. The rolling bearing of claim 1 wherein the radiusof curvature of said convex surfaces of said semicircular guideways isless than the radius of curvature of the bore of said cage.
 6. Therolling bearing of claim 1 wherein said first guideways have radiallyinwardly extending slots.
 7. The rolling bearing of claim 1 wherein saidrecesses in said end rings are open to the axial ends of said end ringstoward said outer sleeve.
 8. The rolling bearing of claim 1 whereinadjacent side walls of first and second guideways of a pair of guidewayshave parallel sides in planes at an acute angle to the plane defined bysaid common axis and said bearing axis.
 9. The rolling bearing of claim1 wherein the centers of said second guideways are closer to the planedefined by the corresponding common axis and said bearing axis than thecenter of the corresponding first guideway.